Lead Exposure Eyed as Risk for Cataracts

Dec. 7, 2004 -- Lead exposure may increase the risk of cataracts, especially for men, a new study shows.

Despite public health efforts to cut lead in gasoline, paint, and other sources in the environment, lead exposure continues to pose a significant problem, writes researcher Debra A. Schaumberg, ScD, MPH, with the preventive medicine division at Brigham and Women's Hospital in Boston.

In fact, "most adults continue to have substantial body burdens of lead," she writes in her report. It appears in this week's issue of the Journal of the American Medical Association (JAMA). More than 90% of the total body burden of lead is accumulated in the bones, where it is stored. Lead stays in bones for up to 10 years where it can be slowly released and can affect other organs. Although over time, lead naturally becomes inert (harmless) to some extent, lead that remains will circulate through the bloodstream, Schaumberg explains.

Much evidence has indicated that accumulated lead exposure increases the risk of several chronic disorders, including hypertension and mental decline. As with other pollutants and toxins, the cell damage comes from unstable radicals created by lead exposure.

Studies have also shown that lead exposure could cause age-related cataracts, the leading cause of blindness and visual impairment worldwide, writes Schaumberg.

Schaumberg's study involved 642 men -- all about 69 years old -- who had leg bone measurements indicating lead exposure. Researchers also looked at the men's medical records for information on eye cataracts.

They found 122 cases of cataracts among the men. Men with high bone levels of lead were significantly more likely to have cataracts, she reports. The link was still strong, even when other risk factors, such as smoking and diabetes, were taken into account.

Men had more than a 2.5-fold increased risk of cataracts if they had the highest levels of lead in their bone compared with men with the lowest lead levels, she writes.

Because lead constantly circulates throughout the blood system at very low levels (which are difficult to measure), other tissues in the body are exposed, Schaumberg explains.

Lead exposure can damage cells in a variety of ways, leading to protein buildup on the lens and interfering with calcium absorption, which keeps the lens clear. Lead has even been found in cataracts removed from eyes.

Based on the researchers' estimates, 42% of cases of cataracts in the study were attributed to lead exposure. Schaumberg adds that although blood measurements for lead were analyzed, this measurement did not correlate with cataract risk. This may be because blood levels of lead reflect only recent exposures.